All Genetic Epidemiology Branch investigations evaluate the contributions of host susceptibility and environmental exposure in the development of cancer. A broad range of study designs are utilized, varying from family studies for linkage analysis, to biochemical epidemiology studies, to more classical case-control and cohort studies. Most investigators included a laboratory component. To facilitate efforts in gene mapping, a formal agreement with the Laboratory of Viral Carcinogenesis has been established and is functioning well. This year, genetic heterogeneity was demonstrated in the melanoma-prone families, with some families linked to 1p36, some to 9p21-22, and some to both. A new familial clustering of tumors, Ewings sarcoma family of tumors, melanoma, brain, and stomach cancers was described. The CYP2D6 phenotype and genotype did not appear to be associated with lung cancer risk in a case-control study of lung cancer. Second lung cancers were linked to continued cigarette smoking, and to a lesser extent, chest irradiation. The risk of myocardial infarction after Hodgkin's disease is 3-fold increased overall and is related to mediastinal radiation. The risk is over 40-fold in- creased in those irradiated before age 20. New investigations of the familiarity of dysplastic nevi and of Beckwith-Wiedemann syndrome were initiated.